[ kuh-men-suh-liz-uhm ]


  1. Ecology. a type of relationship between two species of a plant, animal, fungus, etc., in which one lives with, on, or in another without damage to either.
  2. Sociology. peaceful coexistence among individuals or groups having independent or different values or customs.


/ kə-mĕnsə-lĭz′əm /

  1. A symbiotic relationship between two organisms of different species in which one organism derives benefit while the other is unaffected. Examples of commensalism include epiphytic plants, which depend on a larger host plant for support but which do not derive any nourishment from it, and remoras, which attach themselves to sharks and feed on their leavings without appreciably hindering their hosts.
  2. Compare amensalism

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Word History and Origins

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Compare Meanings

How does commensalism compare to similar and commonly confused words? Explore the most common comparisons:

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Example Sentences

In Hemileia it was ruthless parasitism; in Strigula advantageous commensalism.

Mr. A. Agassiz has remarked to me another example of commensalism.

Remarkable cases occur of commensalism between certain crabs and sea-anemones, and they betoken much intelligence.

But the precise limit at which commensalism begins is not always easily to be ascertained.

Another case of commensalism has been made known to us by Professor Reinhardt of Copenhagen.


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More About Commensalism

What does commensalism mean?

Commensalism is a relationship between two species of organisms, such as plants, animals, and fungus, in which one species benefits while the other is unaffected, as in Scientists have studied the commensalism of fleas that feed on birds’ feathers. 

A well-known example of commensalism is the relationship between the remora, commonly known as a suckerfish, and a shark. The  remora uses its suction cup–like head to attach itself to a shark. The remora benefits from the speed, protection, and leftover food from the shark. The shark gets nothing from the remora. It isn’t hurt by the remora, but the remora doesn’t help the shark in any way.

You can think of commensalism as a “+/0” relationship: One species benefits while the other remains the same. This is what sets commensalism apart from the other types of relationships between organisms, such as mutualism, parasitism, and amensalism.

In mutualism, both species benefit from the relationship. For example, a bird might pick food out of the teeth of an alligator, which prevents the teeth from becoming infected. Mutualism is a “+/+” relationship because the bird gets food to eat and the alligator gets cleaner teeth.

In parasitism, one species (the parasite) benefits at the expense of the other species, a “+/-” relationship. For example, when a  mosquito bites you, it has drunk some of your blood, which nourishes it. You, however, get an itch bite and possibly a disease carried by mosquitoes, such as Eastern equine encephalitis (EEE).

In amensalism, one species harms another species while remaining unaffected, a “-/0” relationship. For example, the black walnut tree secretes a substance that is harmful to other plants. The tree isn’t harmed by either the substance or the other plants.

Why is commensalism important?

The first records of the word commensalism come from around 1870. It combines commensal, meaning “living with, on, or in another without either being harmed,” and the suffix -ism, which creates nouns that denote an action or practice.

Commensalism happens frequently in nature. For example, an animal might seek shade underneath a large tree or a small animal might stay near a larger herbivore to discourage predators. The key to commensalism is that one species (called the commensal) benefits in some way, while the other isn’t affected, as when a monkey rides on an elephant to travel faster and safer.

Did you know ... ?

Commensalism also occurs between humans and other organisms. Some examples include bacteria that live inside us but don’t harm or help us and tiny mites that eat our dead skin or hair.

What are real-life examples of commensalism?

The word commensalism is more likely to be used by natural scientists or biology students.

What other words are related to commensalism?

Quiz yourself!

Is commensalism used correctly in the following sentence?

Lice that feed on birds’ feathers without harming the bird is a type of commensalism.